1. Field of the Invention
The present invention relates to a solid-state image pick-up device such as a CCD, and more particularly to a solid-state image pick-up device having a wide dynamic range in which a pixel having a high sensitivity and a pixel having a low sensitivity are arranged.
2. Description of the Related Art
In a solid-state image pick-up device such as a CCD, a large number of photoelectric converting units (which will be hereinafter referred to as photodiodes) such as minute photodiodes for storing an electric charge corresponding to an amount of incident light are arranged vertically and horizontally and the electric charge stored in each of the photodiodes is read to reproduce the image of light formed on the surface of the solid-state image pick-up device in response to an electric signal.
However, there is a problem in that the photodiode constituting each pixel of the solid-state image pick-up device has a certain amount of saturation charges so that electric charges that is beyond the constant amount of incident light cannot be stored, by which a dynamic range becomes small. For this reason, there has been made a trial in which both a pixel having a low sensitivity and a pixel having a high sensitivity are arranged in the solid-state image pick-up device to enlarge the dynamic range.
FIG. 5 is a typical sectional view showing a conventional solid-state image pick-up device. In FIG. 5, a result obtained by simulating the degree of the refraction of an incident ray is shown together. A large number of minute photodiodes 2H and 2L are alternately arranged vertically and horizontally on a silicon substrate 1, and the photodiode 2H is used as a pixel having a high sensitivity and the photodiode 2L is used as a pixel having a low sensitivity. An electrode 3 for transferring an electric charge stored in each pixel and a shielding film 4 covering the electrode 3 are provided on the surface of the silicon substrate 1.
A color filter layer 5 and a microlens layer 6 are provided on the silicon substrate 1. A microlens 6H for a pixel having a high sensitivity and a large area and a microlens 6L for a pixel having a low sensitivity and a small area are convexed over a microlens layer 6, and the microlens 6H for a pixel having a high sensitivity collects light incident on a large area in the photodiode 2H and the microlens 6L for a pixel having a low sensitivity collects light incident on a small area in the photodiode 2L. The microlens layer 6 having such a structure has been described in JP-A-11-177073, for example.
In recent years, the number of pixels of a solid-state image pick-up device reaches several millions and the microlens layer 6 to be mounted on the solid-state image pick-up device has also been finer. The microlens layer 6 is generally manufactured by a photoetching technique and it is necessary to change the thicknesses of the microlenses 6H and 6L in order to cause the focal lengths of the microlens 6H for a high sensitivity and the microlens 6L for a low sensitivity having different areas to be equal to each other. Therefore, there is a problem in that the manufacture cannot be carried out at a one-time photoetching step and the photoetching step is to be carried out many times, resulting in an increase in a manufacturing cost.
For this reason, conventionally, the manufacture is carried out by setting the thickness of the microlens 6H for a high sensitivity to be equal to that of the microlens 6L for a low sensitivity as shown in FIG. 6. To the contrary, the manufacture is carried out by setting the thickness of the microlens 6L for a low sensitivity to be equal to that of the microlens 6H for a high sensitivity as shown in FIG. 7. Thus, the manufacturing cost of the microlens layer 6 is reduced.
As in the simulation of a pencil of light in FIGS. 6 and 7, however, there is a problem in that a condensation efficiency into the photodiode 2H for a high sensitivity is reduced in FIG. 6 and a condensation efficiency into the photodiode 2L for a low sensitivity is reduced in FIG. 7, and the light incident on the solid-state image pick-up device cannot be distributed efficiently into the pixel for a high sensitivity and the pixel for a low sensitivity.
It is an object of the invention to provide a solid-state image pick-up device which can be manufactured at a low cost and can efficiently distribute incident light into a pixel for a high sensitivity and a pixel for a low sensitivity.
In order to attain the object, the invention provides a solid-state image pick-up device in which a microlens layer is provided on a surface side of a semiconductor substrate having photoelectric converting units for storing an electric charge corresponding to an amount of incident light arranged vertically and horizontally, wherein a microlens to be provided on the microlens layer is disposed on only the photoelectric converting unit to be used as a pixel having a high sensitivity and the microlens layer in a position facing the photoelectric converting unit to be used as a residual pixel having a low sensitivity has a planar or perforated structure.
By this structure, the incident light can be distributed efficiently into each of the photoelectric converting units having the pixel for a high sensitivity and the pixel for a low sensitivity, and the incidence efficiency of the light incident on each photoelectric converting unit can be enhanced, and furthermore, the microlens layer can be manufactured at a low cost.
In the foregoing, it is preferable that a separate convex lens layer from the microlens layer which is provided with a convex lens for collecting, into the photoelectric converting unit, light incident on the photoelectric converting unit to be used as at least the pixel having a low sensitivity should be interposed between the microlens layer and the semiconductor substrate. By this structure, the incidence efficiency of the light incident on the photoelectric converting unit to be used as the pixel for a low sensitivity can further be increased, and furthermore, the microlens layer and the convex lens layer can be manufactured at a low cost.
In the foregoing, furthermore, it is preferable that the convex lens of the convex lens layer should be provided to be convexed on the semiconductor substrate side and the convex lens of the convex lens layer should be provided to be convexed on the incident light side, and furthermore, the convex lens layers of the lower convex lens and the upper convex lens should be provided and interposed between the microlens layer and the semiconductor substrate. By this structure, it is possible to further reduce the manufacturing cost of the solid-state image pick-up device by utilizing the convex lens layer having a low manufacturing cost.